Polyimides, such as those prepared according to Edwards, U.S. Pat. No. 3,179,614, are useful in a wide variety of commercial applications. The outstanding performance characteristics of these polymers under stress and at high temperatures have made them useful in the form of bushings, seals, electrical insulators, compressor vanes and impellers, pistons and piston rings, gears, thread guides, cams, brake linings, and clutch faces. While basically non-melt fabricable, these polyimide resins can be molded into the desired final shape by specialized fabrication techniques.
It is often desirable to incorporate fillers in such polyimide compositions before fabrication into their final form. For example, the admixture of graphite in a polyimide intended for a bearing surface gives a lubricating effect which improves the wear characteristics of the final product. The graphite is typically incorporated in the course of preparation of the polyimide by precipitation of the polyimide resin on the graphite particles.
While the addition of graphite to polyimides has contributed significantly to the wear characteristics of the final polyimide product, incorporation of graphite also has generally resulted in a depreciation of physical properties under prolonged exposure to high temperatures. Specifically, the polyimide exhibits an undesirable weight loss, shrinkage, and loss of tensile strength and elongation.